The xVIO back-end performs MSCKF [1]} updates. MSCFK minimizes the residual between tracked feature points and the back-projection on the camera plane of the triangulated landmark. Figure REF  represents how the MSCKF residuals can be interpreted in a collaborative setup. The tracked landmark \({}^w{p_j}\)  is triangulated by using all the measurements of robots' cameras, \(^ic^0\)  and \(^ic^1\) . Then the resulting 3D point is projected into the camera planes that observed the feature.
